Roofing system components work like a crew, not a pile of parts: seven parts, each with one job, stacked in an order that sends water down and out while letting air move up and through.
From the street you see shingles. Under and around them sit six more roofing system components, all fastened to the roof deck, the wood structure everything sits on.
This guide takes the roof apart like an assembly drawing: what each component does, where it goes, what Ohio’s code says and what failure looks like.
Water runs down, air runs up, and every part overlaps the one below it. Leak barrier, underlayment, starter strip, shingles, flashing, hip and ridge cap and balanced attic vents, all on a sound deck. Skip one of the roofing system components and the rest fail sooner.
What’s In This Guide
How Roofing System Components Work Together
Think of roofing system components as overlapping shingles of protection. Every part sheds water onto the part below it, never behind it, so install order matters as much as materials.
Water is only half the story. Air enters low at the eaves and leaves high near the ridge, carrying out heat and moisture. Roofing system components that shed rain but trap damp air can still rot from the inside.
- Leak barrier. Self-sealing membrane at eaves and valleys.
- Underlayment. Roof deck protection across the rest of the roof.
- Starter strip. Seals the first course along the edge.
- Shingles. The visible, weather-facing surface.
- Flashing + edge metal. Metal at walls, chimneys, valleys, pipes and the drip edge.
- Hip & ridge cap. Finishes and seals the peaks.
- Attic ventilation. Balanced intake low, exhaust high.
Take the Roof Apart, One Part at a Time
Tap any of the seven roofing system components to lift it out of the stack and see its job, its place and its failure signs.
Leak Barrier
Component 1 of 7- Its job
- A self-adhering ice & water membrane that seals around nails and stops ice-backed water.
- Where it goes
- Eaves, to at least 24 inches inside the wall line where code requires, and valleys.
- Failure looks like
- Ceiling stains near outside walls after a snowy stretch.
Underlayment
Component 2 of 7- Its job
- Roof deck protection that backs up the shingles in wind-driven rain.
- Where it goes
- The rest of the deck: one layer at 4:12 or steeper, two from 2:12 to 4:12.
- Failure looks like
- Leaks only in sideways rain.
Starter Strip
Component 3 of 7- Its job
- Puts a sealant line under the first course so the edge can’t lift.
- Where it goes
- Eaves, often rakes, before the first course.
- Failure looks like
- A bottom row that flaps in wind.
Shingles
Component 4 of 7- Its job
- Takes the sun, rain, hail and wind.
- Where it goes
- On top, nailed in the marked nailing zone.
- Failure looks like
- Missing tabs, heavy granule loss or curled edges.
Flashing + Edge Metal
Component 5 of 7- Its job
- Metal that bridges gaps shingles can’t, plus drip edge that kicks water clear of the fascia.
- Where it goes
- Sidewalls, roof-wall corners, chimneys, valleys, pipes, eaves and rakes.
- Failure looks like
- Stains below a chimney, rotted siding under a corner or stained fascia.
Hip & Ridge Cap
Component 6 of 7- Its job
- Pre-bent caps that seal the peak and cover the ridge vent.
- Where it goes
- Every ridge and hip.
- Failure looks like
- Cracked or missing caps.
Attic Ventilation
Component 7 of 7- Its job
- Intake and exhaust that move air through the attic to clear heat and moisture.
- Where it goes
- Intake in the soffits, exhaust near the ridge.
- Failure looks like
- Winter frost on the deck or ice dams at the eaves.
What Ohio’s Code Says About the Hidden Parts
Several roofing system components aren’t optional. The Residential Code of Ohio’s roof assemblies rule spells out where they go. Here’s what to know before comparing bids.
| Component | The number | What the code says |
|---|---|---|
| Ice barrier at eaves | 24 in. | Where ice has backed up water at eaves, it runs to at least 24 inches inside the exterior wall line. |
| Underlayment | 1 or 2 layers | One layer at 4:12 or more; two from 2:12 up to 4:12. |
| Shingle slope | 2:12 min. | Asphalt shingles only on 2:12 or steeper. |
| Valley lining | 24–36 in. | Open metal valleys: 24-inch lining. Closed valleys: 36-inch roll roofing. |
| Roof-wall corner | Required | Flashing must divert water where an eave meets a sidewall. |
| Chimney cricket | Over 30 in. | A cricket goes uphill of any chimney wider than 30 inches. |
| Tear-off vs. layover | 2 layers | No recover over two or more coverings; replacement goes to the deck. |
Local note: the ice barrier rule applies where your building department designates a history of ice damming. Even where it isn’t required, a leak barrier at eaves and valleys belongs on any list of roofing system components you compare.
Ventilation Is One of the Roofing System Components You Can’t See
The International Code Council’s R806.2 sets the minimum net vent area at 1/150 of the attic floor. It drops to 1/300 when 40 to 50 percent of that area sits in the upper attic, no more than 3 feet below the ridge, with the rest at the eaves.
The Department of Energy’s Building America Solution Center describes the same high-low split. Low vents pull air in; high vents let it out. Of all the roofing system components, these two only work as a pair.
- Soffit intakeFresh air enters under the eaves.
- Clear channelInsulation stays back so air can reach the deck.
- Attic sweepAir rises under the deck, picking up heat and moisture.
- Ridge exhaustAir leaves at the peak, under the ridge cap.
A 1,500 sq. ft. Attic
At 1/300, that’s 5 square feet, or 720 square inches, of net vent area: about 288 to 360 at the ridge, the rest in the soffits. At 1/150, double it.
Flashing: Where Most Leaks Start
Shingles cover flat planes well. Leaks start where the plane stops: at a wall, a chimney, a valley or a pipe. Flashing is where roofing system components meet everything else.
Step Flashing
Beside a wall, Ohio’s code calls for continuous or step flashing that directs water onto the roof or into the gutter, one piece per shingle course.
Kickout Flashing
InterNACHI says a kickout diverts water from the siding into the gutter, and that a missing one can hide severe wall damage.
Wrapped + Cricket
Chimney flashing follows the shingle maker’s instructions. Uphill of a chimney wider than 30 inches, a cricket splits the water away from the brick.
Lined Valleys
A valley drains two roof planes at once, so it gets a lining before any shingles go down, with leak barrier underneath.
After a storm, check flashing first. Our guide to Dayton wind damage shows what lifted metal looks like.
Why Matched Roofing System Components Matter for the Warranty
Manufacturers design roofing system components to be tested and installed together. That’s the idea behind a system warranty.
GAF lists seven parts in its Lifetime Roofing System: leak barriers, roof deck protection, starter strip shingles, Lifetime shingles, attic ventilation, rooftop accessories and ridge cap shingles. Install a Lifetime shingle with at least three qualifying GAF accessories, and GAF’s Lifetime limited warranty covers the shingles and those qualifying accessories.
Parts from another brand don’t count toward those three. Ask which warranty your exact mix of roofing system components qualifies for, in writing.
Choosing the shingle itself? Our durable roofing material guide compares the options for Ohio weather.
GAF Lifetime Roofing System
As a GAF President’s Club Contractor, Thrush & Son® installs GAF Timberline HDZ, Timberline UHDZ, Timberline AS II, Camelot II and Slateline shingles with matching GAF system components.
Signs a Component Got Skipped
Most missing roofing system components show up on paper before they show up on the ceiling.
- The bid only says “shingles.” A real scope lists all seven roofing system components.
- A layover on a roof with two layers. Ohio’s code doesn’t allow a new covering over two or more existing ones.
- No plan for the roof-wall corners. If kickouts aren’t mentioned, ask.
- Ridge vent with no intake. Exhaust without soffit intake can’t move air.
- “Same warranty” on mixed parts. Ask which system warranty the exact parts qualify for.
Checking a roof after hail instead? Start with our signs of hail damage walkthrough.
The Takeaway Worth Sharing
A roof isn’t shingles. It’s seven roofing system components that hand water down and air up. When you compare bids, compare all seven.
Send this to the neighbor who’s comparing roof quotes this season.
Want Every Part Done Right? Let’s Talk Roofs
Thrush & Son®: family-owned exterior pros since 1960.
If you’re in the Miami Valley and want every roofing system component installed as one matched assembly, read the Thrush & Son® guide to roofing components, then book an estimate.
➡️ Schedule in Dayton➡️ View All ServicesCall (937) 833-5136 · 115 Jefferson St, Brookville, OH 45309
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Further Reading
Official sources: the Residential Code of Ohio, roof assemblies, the International Code Council (IRC R806), the U.S. Department of Energy’s Building America Solution Center and InterNACHI.
Roofing System Components FAQ
What are the main roofing system components?
The main roofing system components are the leak barrier, underlayment, starter strip, shingles, flashing with drip edge, hip and ridge cap and balanced attic ventilation. All seven sit on the roof deck, and each overlaps the one below it.
Is ice and water barrier required in Ohio?
The Residential Code of Ohio requires an ice barrier where there has been a history of ice backing up water at the eaves. It must run from the roof edge to at least 24 inches inside the exterior wall line.
How much attic ventilation does a roof need?
The model code baseline is 1/150 of the attic floor area in net vent area. It can drop to 1/300 when 40 to 50 percent of the vents sit high, within 3 feet of the ridge, and the rest are low at the eaves.
Can I put new shingles over my old roof?
Not if the roof already has two or more layers. Ohio’s code bars recovering in that case, and a tear-off lets the crew inspect the deck and install all the roofing system components fresh.
Does mixing brands affect my roof warranty?
It can. System warranties count only that manufacturer’s qualifying parts. GAF, for example, requires a Lifetime shingle plus at least three qualifying GAF accessories for its Lifetime Roofing System coverage.
Written by Corey Thrush, Vice President and third generation of Thrush & Son®.
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